The present disclosure relates to a light emitting device, a light emitting device package, and a lighting system.
The light emitting device is a semiconductor device for converting electric energy into light energy and may realize various colors by adjusting a composition ratio of a compound semiconductor.
The light emitting device emits light when electrons injected from an electron injection layer and electron-holes injected from an electron-hole injection layer are combined in an active layer.
Meanwhile, when the active layer of the light emitting device is close to a reflective mirror with high reflectivity, luminescence distribution may vary according to the distance between the active layer and the reflective mirror. For example, in a case of a vertical GaN Light Emitting Diode (LED), when a P—GaN and ohmic layer is disposed between Ag (corresponding to the reflective mirror) and Multi-Quantum Wells (MQWs) (corresponding to the active layer), the luminescence distribution of the MQWs of the active layer may be adjusted according to the thickness of the p-GaN and ohmic layer.
However, the reflective mirror may not be necessarily limited to metal. Actually, since luminescence distribution is adjusted with high reflectivity in a vertical direction, when a mirror of a dielectric layer such as Distributed Bragg Reflectors (DBRs) is disposed around the active layer, a similar phenomenon occurs.
Accordingly, if the distance between the active layer and the reflective mirror satisfies a constructive interference condition, the luminescence distribution of the MQWs is provided based on a vertical direction and this may improve extraction efficiency.
However, the extraction efficiency obtained by adjusting luminescence distribution through interference effect is effective when the thickness of the active layer is less than λ/n. If the thickness of the active layer is greater than λ/n, constructive and destructive conditions become uniformly distributed in the active layer so that extraction efficiency becomes identical to that of an average state (i.e., when there is no interference effect). However, if the active layer becomes thinner for interference effect, a reliability issue is raised due to the increase of leakage current.